The present invention relates to an image forming apparatus and an image forming system.
In recent years, in color multi-function copying machines and color printers, a specific pattern (prosecution patter), which human cannot recognize, is added to an outputted matter so as to prosecute a source of the matter when copying a prohibited document such as a paper currency or a document of value is copied.
On the other hand, the above color image forming apparatuses have been used as digital printing machines in a field of printing a wide variety in small quantity (high-mix low-volume printing), and a system provided with a post-processing apparatus having functions of perforation, stitching, folding and cutting is becoming popularly. (for example, Patent Document 2)    Patent Document 1: Tokkaihei 4-294682    Patent Document 2: Tokkai 2003-95533
In case post-processing is carried out for the outputted matter having the specific pattern, it was found that the following problems occur.
For example, in case a plurality of the outputted matters are stacked and cut, the specific patterns formed in the same position of respective outputted matters forms lines which are noticeable on a cutting surface. Also, for example, in case the plurality of the outputted matters are folded and stacked, the specific patterns formed in the same position of respective outputted matters are connected and forms the line which are noticeable.